1. Technical Field
The present disclosure relates generally to the field of ballistic materials and composites for defeating ballistic projectiles, and methods of making the same. More particularly, the present disclosure relates to the use of polyurea hybrid composites for those purposes.
2. Related Art
Conventional ballistic materials are often utilized in ballistic vests and in other armor applications to protect military personnel and law enforcement officers from injury or death from ballistic impact trauma. Desirable characteristics of ballistic materials include an ability to absorb the energy of projectiles across a large surface area and slow it down, hardness to destroy the projectile and prevent penetration of fragments, light weight to reduce fatigue from wear, and flexibility or malleability to permit diverse applications and preserve a wearer's mobility.
Existing ballistic materials involve trade-offs between these desired characteristics. For example, modern ballistic vests are principally made from many layers of woven or laminated synthetic fibers, such as para-aramid (Kevlar) or ultra-high-molecular-weight polyethylene (Dyneema). These materials are lightweight and flexible, and will prevent penetration from some handgun rounds. However, ballistic vests made from these materials alone are generally ineffective against large caliber handgun rounds or rifle rounds, and even if a bullet is prevented from penetrating the vest, the wearer may still suffer severe blunt trauma due to back face deflection.
To reduce the effects of back face deflection and to add protection against large caliber pistol rounds and rifle rounds, trauma plates are often utilized in ballistic vests. Metal trauma plates are generally considered to be superior at reducing trauma from back face deflection and at stopping impacts from multiple rounds, but come at the cost of a significant weight increase to the ballistic vest. Ceramic trauma plates are generally considered to be more lightweight than metal trauma plates, but are generally considered to be less effective at stopping impacts from multiple rounds and reducing blunt trauma from back face deflection. Additionally, these materials have a risk of spallation after impact, and often require placement of additional synthetic fiber materials or rubberized coatings on the rear surface to catch any potential spall. Regardless of the construction and material used, however, ballistic vests with trauma plates are significantly heavier than those without, and the protection from a stiff trauma plate cannot extend to areas where flexibility is important without significantly impacting mobility when worn.
The National Institute of Justice promulgates standards for body armor, and classifies five levels of protection (IIA, II, IIIA, III, IV) ranked by ballistic performance. Type IIA armor is rated to protect from 9 mm and .40 S&W bullets. Type II armor is additionally rated to protect from .357 Magnum bullets. Type IIIA armor is further rated to protect from .44 Magnum bullets. Type III armor, which usually includes trauma plates, is rated to protect from up to 7.62 mm rifle bullets. Finally, Type IV armor is rated to protect against up to .30 caliber armor piercing bullets. Law enforcement officers, in the absence of any specific threats or special duties, will typically wear Level IIA or II vests, with vests offering higher grades of protection reserved for special situations or duties justifying additional protection at the cost of added weight and restriction to the wearer's mobility.
Recently, research by the U.S. Navy has revealed the utility of polyurea composite coatings for the purpose of defeating ballistic projectiles. For example, U.S. Pat. No. 8,580,387 describes the utility of a polyureas as a strike surface layer or a spall liner in combination with ceramic or metal armors. Specifically, it was found that a ballistic polyurea coating may be obtained as the cured reaction product of isocyanate and a mixture of two diamines having the general formula H2N—Ph—(C═O)—O—(CH2—CH2—CH2—CH2—O)n—C═O)—Ph—NH2, the first having a value of n between 13 and 14 and the second having a value of n between 2 and 3, in a ratio of 1:0.58 to 1:0.91 by weight. These investigations, however, only scrape the surface of the potential of ballistic polyurea composites, and are largely concerned with vehicle and ship armor. The area as a whole, especially with regards to ballistic vests, remains relatively unexplored.
Consequently, there is a need for improved ballistic polyurea composites for defeating ballistic projectiles.